By means of working so-called impact resistant modifiers into brittle polymers, these can be improved decisively with respect to their toughness. The modification of impact resistance occurs usually by means of distributing, when the material is in a molten state, smaller constituents of a tough elastic polymer component having a low glass temperature into a greater portion of a different polymer or of a similar less tough polymer. The resulting alloy of polymers is a chemical blend or an alloy, and it has completely new properties in comparison with the original polymers. The modified new properties concern, besides the toughness, the viscosity, the strength, the hardness, the dimensional stability under heat, the creep tendency, the resistance against chemicals, the dimensional stability and others as well.
By working a second, e.g. an olefinic polymer phase, into a continuous polyamide matrix, the appearance and the surface properties are also being changed. Mostly surfaces of a white coloration or a mother-of-pearl structure are generated. In this process, transparent polyamides lose their transparency, one of their frequently most desired properties. Such impact resistant products are described in EP 0 073 036, in EP 191 548 or, more generally, in DAS 1 341 606.
By compounding of certain kinds of tough and transparency-compatible polymers, transparent polyamide alloys can nevertheless be obtained because of equal indices of refraction of the two phases. Thus, it is known that cladded-core polymers, such as methacrylate butadiene styrol copolymers, which are mentioned in JP 04 337 355, or that certain polyester amides, e.g. those made from polyamide 12 and caprolactone with other polyamides, which themselves contain polyamide 12 segments in a polymeric chain structure or that reactive polycarbonates with amorphous polyamides, e.g. of the type PA 61/6T, produce impact resistant, transparent polyamide blends.
From the EP 0 628 602 A1 transparent polyamides are known, which are built up from a semi-crystalline and thus cloudy or opaque amide and an amorphous polyamide. The resulting polyamide is, it is true, likewise transparent, but it has inadequate properties with respect to toughness and elongation and the dimensional stability under heat.
A further possibility for increasing the impact resistance of brittle transparent polyamides consists in adding to them by means of additional polymerization, for example, long-chain monomers by means of compounding, which improve the toughness, or by alloying them by means of compounding a tougher partially crystalline polyamide, as it is described in the patents U.S. Pat. No. 4,404,317, where polyamide 66, or in DE 2 642 244 where polyamide 12 or in U.S. Pat. No. 5,266,655 where polyamide 6 are added in an alloying process to amorphous copolyamides. By these measures, however, many particular properties of the original polyamides are often changed too much or many a desirable individual property, such as the transparency, is being lost or the appropriate monomers are not available in the required purity, amount or price.
It is, therefore, the objective of the present invention to propose new polyamide alloys, which essentially maintain the preferred properties of the original polyamides and improve in particular the toughness and elongation properties.
The present invention describes a transparent polyamide alloy, with a TG of  greater than 120xc2x0 C. The polyamide is produced by compounding from 70-98% by weight of a transparent, amorphous, rigid and/or brittle polyamide A with a glass transition point of at least 180xc2x0 C. containing not more than 25 mol % of a lactam or a xcfx89-aminocarbonic acid with a carbon number of 6-12, at least 35 mol % of a cycloaliphatic diamine, and dicarbonic acids, excepting terephthalic acid, and 2-30% by weight of a transparent, amorphous, impact resistant polyamide B with a glass transition point below 90xc2x0 C., containing 50-80 mol % of at least one long-chain lactam or xcfx89-aminocarbonic acid or diamine/dicarbonic acid pair with more than 10 carbon atoms, and a diamine of C6 carbon atoms and at least 10 mole % terephthalic acid.